Hi Victor,
Conductive anodic filament (CAF) testing is a test where a specific coupon is subjected to 85% relative humidity and 85°C temperature while a bias is applied to two adjacent traces. The resistance is measured and when there is a decade drop in resistance the sample fails. What happens is there is a conductive anodic filament that forms between the adjacent conductors which have typically 100 volt bias.
This test method is called out in IPC TM 650 2.6.26 Conductive Anodic Filament (CAF) Resistance Test: X-Y Axis.
The point is that the crazing provides a path for the formation of CAF and there is conductive moisture, from the copper plating bath, that is trapped in the space between the epoxy and the glass. This makes CAF much more likely to form.
One needs four things in order to have CAF formation. One needs a path; moisture, a bias between adjacent conductors, and ionic contamination. The moisture may be the humidity that is in the end use environment. Typically there is condensation on the circuit board with temperature fluctuations that provides extra moisture. The ionic contamination comes from the trapped plating liquid. The path is form the crazing. The bias is provided by normal functioning of the circuit board.
This is why I think that crazing should be able to be evaluated by microsectioning and not limited to visible surface defects as it is implied in IPC A 600.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
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________________________________
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: December 16, 2013 7:50 AM
To: Paul Reid
Cc: [log in to unmask]
Subject: RE: [TN] Crazing - the pictures
Paul,
Can you elaborate more on CAF Testing.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Friday, December 13, 2013 3:05 PM
To: [log in to unmask]
Subject: Re: [TN] Crazing - the pictures
Hi Wayne,
I agree with your wager. I think that they will fail CAF testing.
The fabricator does not want to pursue CAF testing as it might confuse the argument.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: December 13, 2013 2:17 PM
To: [log in to unmask]
Subject: Re: [TN] Crazing - the pictures
By the way, I'll wager that 85/85/85 testing with voltage bias will fail these units. (for the unfamiliar, that's 85C 85%RH, 85hrs). Applying the bias may be a bit problematic with unpopulated boards, but I'm sure you can come up with something reasonable.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Friday, December 13, 2013 12:49 PM
To: [log in to unmask]
Subject: [TN] Crazing - the pictures
Hi Everyone,
I finally found Steve Gregory's email address. He has kindly posted some the pictures of the crazing that I found.
http://stevezeva.homestead.com/6494_2_1_mod.jpg
http://stevezeva.homestead.com/6494_M_001.jpg
http://stevezeva.homestead.com/6496_2_10.jpg
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask]
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